1. Field of the Invention
This invention relates to surgical instruments, and in particular to an improved trocar for providing communication with a body cavity.
2. Description of the Relevant Art
Trocars are very useful surgical instruments that essentially comprise a trocar tube or cannula, which surrounds an obturator (styler) having a sharp point tip or tip on the distal end thereof. The trocar assembly thus described is manually forced by the surgeon with the sharp point or tip serving to pierce the body wall so as to admit the surrounding trocar tube. After the tube is in communication with the body cavity, the obturator is removed and various instruments may be inserted into the cavity through the trocar tube. One such application is to insert an endoscopic instrument for performing endoscopic surgery within the cavity.
A common problem with early trocars was the danger associated with an unprotected piercing tip of the obturator. Being very sharp, the tip can cause injury to the surgeon if unprotected prior to use. During use, the obturator and trocar tube are forcibly thrust through a body wall until the tube is within the body cavity, so as to provide access thereto from the body exterior. After performing its function of piercing the body wall to admit the tube, the sharp tip may cause damage to body tissue and organs within the cavity.
In order to solve these and other problems, trocars have been developed that have spring-loaded tubular shields that normally protect and cover the sharp pointed tip until and incident to the trocar tube being thrust through the body wall tissue. Two such prior art trocars are shown in U.S. Pat. No. 4,601,710 to Moll and U.S. Pat. No. 4,654,030 to Moll, et al. With the devices of these patents, the surrounding trocar tube is forced in a proximal direction against a biasing spring incident to passing through the body wall tissue so as to expose the pointed tip, which is normally recessed just inside the open distal end of the trocar tube. Once through the body wall, the force on the trocar tube diminishes and it is forced in a distal direction by spring force until it again covers the tip. It thus covers the sharp pointed tip within the body cavity and thereby protects against injury. A locking mechanism may also be provided so that the trocar tube may not be accidentally retracted.
A problem with this just-described prior art device is that the trocar tube must move distally against tissue resistance in order to cover and protect the tip within the body cavity. Another problem is that a fairly high penetration force is required.